1. Field of the Invention
This invention relates to a display device and a vehicle based thereon.
2. Background Art
To increase display brightness is important in improving display visibility. However, simply increasing display brightness incurs increased power consumption and hence may be impractical. Thus, it is investigated to improve brightness by limiting the display area, or the spatial region of visible display. For example, in a known display device using a high-brightness light source with low power consumption, such as a laser, the visible spatial region is limited by interposing a microlens array sheet, for example, between the laser light source and the viewer and suitably designing the optical characteristics of this microlens to control the divergence angle of laser light, control the visible spatial region, and improve display brightness without adversely affecting the power consumption. However, irradiation of a microlens array sheet with coherent light such as laser light causes speckles to be visible, and is impractical.
On the other hand, for example, head-up display (HUD) displays various traffic information through the windshield of a car on the external background field. For such a head-up display, JP-A 2-195388 (Kokai) (1990) proposes a technique to reduce speckles by vibrating a diffusion plate interposed in the optical path of laser light. However, this method involves a complicated structure because the diffusion plate is vibrated, and was unsuccessful in completely removing speckles. Furthermore, because the diffusion plate cannot control the divergence angle of laser light, this method of using the diffusion plate is not applicable to improving HUD visibility by controlling the spatial region of visible display for traffic information within a certain extent (for example, controlling it so that the display is visible to only one eye).